This invention relates to antennas and antenna elements comprised of patch dipoles and to a new form of circularly polarized patch antenna.
It is generally known by those practicing antenna design that a flat microstrip or patch dipole antenna arranged parallel to and in close proximity with a ground plane conductor will exhibit a broad side antenna pattern. If two such dipoles are arranged in the same closely spaced relationship parallel to a ground plane conductor and separated from one another by a quarter wave length of their operating frequency and have their feed points connected through a quarter wave length phase delay, the two dipoles will form an end firing antenna element whose antenna pattern will be linearly polarized and directed generally along the line connecting common phase points of the dipoles and in the direction of the phase delay.
Many applications, particularly those in the aerospace and aeronautical fields, require a low-profile antenna. Those familiar with the art will recognize that an entire group of low-profile antennas has been developed to fulfill this need which comprises the so-called printed circuit or patch antenna. It is a known deficiency of these low-profile antennas that the gain-bandwidth product is much too limited for a variety of applications. As an example, in my patent application entitled "Low Profile Circular Array Antenna and Elements Therefor" having Ser. No. 289,851 filed Aug. 4, 1981, now U.S. Pat. No. 4,414,550, such an antenna displayed 2.0 dB of reactive loss at the two operating frequencies of interest. In addition such an array of patch elements requires an isolated power splitter which is required to feed each group of patches to provide an end fire characteristic. It can readily be seen that there is not sufficient room on the bottom side of the ground plane for two tuners and one power splitter for each element of the array.
It is, therefore, an object of the present invention to devise an antenna element which includes its own double-tuning circuitry and does so within the general confines of the patch or radiator dimensions. One such double-tuned antenna element has been proposed by G. Dubost in his paper entitled "Theory and Experiments of Broad Band Short-Circuited Microstrip Dipole at Resonance," 1979 which comprises an air-dielectric structure in which the impedance transformation required to match a 50 ohm line is provided by a 1/4 wavelength coupled microstrip line printed above the basic airloaded patch. Dubost uses an additional two short circuited 1/4 wavelength microstrip stubs to double tune the reactive component of the input impedance. One disadvantage of this design is that the feed structure is on the upper, non-groundplane surface and must be connected via coaxial cable or other means back down through the groundplane for most applications.
In accordance with the more detailed description contained below, the present invention is best illustrated in the context of an eight (8) element antenna array. Each element contains two patch dipoles and its respective microstrip feeds. Power distribution and patch excitation means are located on the top surface of the ground plane and at right angles feeding into the microstrip feed. Double tuning is provided within each patch so that the gain-bandwidth product is enhanced. More particularly, the invention comprises an antenna for radiating a signal at a predetermined frequency or range of frequencies comprising: a ground plane conductor; a 1/4 wavelength microstrip resonator including shunt means for connecting thereof a first end ground to said ground plane conductor and a second end adapted to receive the signal; a metal 1/4 wavelength radiator having a radiating surface suspended above said resonator by a predetermined distance, said radiating surface, at one edge thereof, electrically connected to said ground plane conductor.
An alternate embodiment of the invention further comprises: a low profile circularly polarized antenna comprising a flat electromagnetically conductive radiator suspended above a ground plane conductor at a predetermined orientation; at least one resonator means for electromagnetically coupling radiation to said at least one radiator means, said at least one resonator partially insulated from and mounted on said ground plane conductor; and means for suspending said radiator at said predetermined orientation above said ground plane including non-electrical and non-magnetical posts.